Finance calculator

Compound interest calculator

Calculate compound interest growth over time — enter principal, rate, compounding frequency, and years to see future value and total interest earned, updated live, as you type.

On this page10 sections

InputsLive

Compounding

Initial principal

Monthly contribution

$/mo

Annual interest rate

Years

yrs

Result

Future value

$37,405

Interest: $15,405 · Invested: $22,000

Future value$37,405

Interest earned$15,405

Total invested$22,000

Growth factor1.7×

Hypothetical projection. Excludes taxes, inflation, and fees. Actual investment returns vary.

Results are estimates. Consult a professional.

How it's calculated

How the compound interest calculator works

Compound interest earns interest on both the original principal and on previously accumulated interest. Unlike simple interest, each compounding period adds to the base that the next period's interest is calculated on — so the balance accelerates over time rather than growing in a straight line.

The calculator handles two scenarios: a lump-sum deposit that grows on its own, and a lump sum combined with regular monthly contributions. The compounding frequency — annual, quarterly, monthly, or daily — sets how often earned interest is folded back into the balance.

FV = PV × (1 + r/n)^(n × t)

With monthly contributions:

FV = PV × (1 + r/n)^(n×t) + PMT × ((1 + r/n)^(n×t) − 1) / (r/n)

n: annual = 1 | quarterly = 4 | monthly = 12 | daily = 365

SEC Investor.gov — Compound Interest Calculator (methodology and definitions).Federal Reserve — Why Saving Matters (power of compound interest in long-horizon saving).

Example

Worked example: $5,000 at 7% monthly compounding for 20 years

Example: $5,000 initial deposit, 7% annually, monthly compounding, 20 years

Jordan deposits $5,000 in a high-yield savings account earning 7% annually, compounded monthly. After 20 years with no further deposits, the balance grows to $20,078. Adding $200 a month raises the final balance to $120,782 — showing how consistent contributions amplify compounding dramatically.

Lump-sum only: FV = 5,000 × (1 + 0.07/12)^(12×20)

= 5,000 × (1.005833)^240

= 5,000 × 4.0159 = $20,078

With $200/mo: FV = 20,078 + 200 × ((1.005833)^240 − 1) / 0.005833

= 20,078 + 200 × 514.52 = $20,078 + $102,904 ≈ $120,782 (combined)

$120,782

Adding $200 a month to a $5,000 starting balance at 7% monthly compounding over 20 years grows to $120,782. Of that, only $53,000 was money paid in — the remaining $67,782 is pure compounding.

Quick reference

Future value of $5,000 at monthly compounding

The table below shows how $5,000 grows with no additional contributions at three common annual rates and four time horizons, all compounded monthly. Longer time and higher rates have a multiplying — not merely additive — effect.

Years	At 5%	At 7%	At 9%
5 years	$6,417	$7,129	$7,911
10 years	$8,218	$10,144	$12,494
20 years	$13,493	$20,078	$29,649
30 years	$22,167	$39,373	$73,397

$5,000 lump sum, no additional contributions, compounded monthly. Source: SEC compound interest calculator methodology.

Practical tips

Tips for making compound interest work for you

The math of compounding rewards two behaviors above all else: starting early and adding consistently. The following tips translate the formula into actionable habits.

Start as early as possible — ten extra years of compounding can double a final balance. A dollar invested at 25 outperforms roughly four dollars invested at 45 at the same rate.
Maximize compounding frequency — daily compounding edges monthly by a small but real amount on the same nominal rate. When two accounts offer the same APR, choose the one that compounds more frequently.
Automate monthly contributions — even $100 a month added to a growing lump sum dramatically changes the outcome over two or three decades, as the worked example above shows.
Compare APY, not APR — the Annual Percentage Yield (APY) already bakes in the compounding frequency, making account comparisons honest. The APY is always slightly higher than the stated APR.
Avoid withdrawals — every early withdrawal resets the compounding base. Leaving compound growth uninterrupted for the full term is what produces the exponential curve visible in the quick-ref table.

Accuracy & limits

Accuracy and limitations

This calculator uses the standard compound-interest formula with the compounding frequency you specify. It assumes a fixed nominal interest rate for the full term and that monthly contributions (if any) are made at the end of each compounding period. It does not account for taxes on interest, inflation, varying contribution amounts, or rate changes over time. Real savings accounts and investment accounts are subject to rate fluctuations, fees, and tax treatment that will affect actual outcomes.

Results are for educational and planning purposes only and do not constitute financial advice. Consult a qualified financial adviser before making investment or savings decisions.

Glossary

Compound interest terms defined

The initial amount deposited or invested before any interest is added.

How many times per year interest is calculated and added to the balance. Common values: annually (1), quarterly (4), monthly (12), daily (365).

The stated yearly rate before compounding. Divide by n to get the per-period rate.

The total balance — original principal plus all accumulated compound interest — at the end of the term.

The effective annual rate after compounding is applied. APY = (1 + r/n)^n − 1. Always slightly higher than the stated APR when n > 1.

A quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes for money to double. At 7%, money doubles in roughly 72 ÷ 7 ≈ 10.3 years.

About

About this compound interest calculator

This calculator runs entirely in your browser — nothing you enter is sent to any server.

Browse more in our finance calculators, or explore the complete library on the free calculators page.

Questions

Frequently asked questions about the compound interest calculator

A compound interest calculator is a free online tool that helps you project how savings grow with interest compounded daily, monthly, or annually — with optional contributions. Compound interest is interest earned on the original principal plus all previously accumulated interest. Over time, the curve steepens — small differences in rate compound into large differences in final balance. It runs entirely in your browser with instant results and no sign-up.

Simple interest is calculated on the principal only. Compound interest is calculated on the principal plus any interest already earned, so the balance grows faster over time. Most savings accounts, CDs, and investments compound.

Yes, but less than you'd think. Going from annual to monthly compounding raises the effective rate slightly; going from monthly to daily adds only fractions of a percent. The big lever is the interest rate itself, not how often it compounds.

The math is exact for the inputs you provide. Real-world balances will differ because actual rates fluctuate, contributions aren't always perfectly regular, and fees or taxes reduce the effective return. Treat the result as a planning estimate.